Uneven Pad Wear Side to Side but Even on Calipers

[TROVERMAN]

Pulling all the wheels on the 95 E320 wagon, I noticed a few things: On one side of the car front (can't remember which now) the pads look good with decent wear left, but the annoying wear light was flashing on the dash. I figured both sides must be wearing equally. On the opposite front side of the car the pads were warn down a lot more, not to the metal part, but definitely to the min thickness or worse. This is surprising considering the car does not pull side to side when braking.
Any ideas as to why? The brakes work perfectly, and are very strong and smooth. No warning lights as to the brakes, except of course the wear light.

Also: Rotors. The front rotors are very shiny and smooth, like brand new, but there is some "lip" on both the inside and outside edges of the rotor surface. This is true for both front rotors. Is this O.K. or do they need to be replaced? I am not the kind of person who replaces rotors just because I am replacing the pads (which will be replaced this weekend) although I have heard the arguments for it.

In the rear there is a different story. The pads on both rear sides look new, and wear is equal for both. No problems there, but the rotors are confusing me. There is no "lip" whatsoever on these rotors, but the surface is not shiny either. It is relatively smooth, but you can see a whole bunch of marks all the way around the rotor where the pad has contacted the surface. The rotor is fairly smooth, though, it is not like the pad is wearing into the surface.
Any idea on the story here?

Last brake question: on this car the ABS system seems to come on quite often. It will come on when there is a snowy covering on the road, or even if the front wheels get into some mud when I am pulling into the driveway. It seems to work fine. It also seems to have a low threshold for speed, like it will work at 5mph. None of my other ABS equipped cars will do this, even the 96 BOSCH ABS equipped Volvo 960 (RWD) In fact, this is the only car I have ever had that has the ABS come on so often.

Any thoughts?

Thanks.